Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $159.44   4.850%   $167.1728   $167.17   $167.15   $167.20  
  Purchase #2 $174.67   7.621%   $187.9816   $187.98   $188.00   $188.00  
  Purchase #3 $74.97   6.541%   $79.8738   $79.87   $79.85   $79.90  
  Purchase #4 $205.33   5.643%   $216.9168   $216.92   $216.90   $216.90  
  Purchase #5 $89.46   6.102%   $94.9188   $94.92   $94.90   $94.90  
  Purchase #6 $28.27   11.529%   $31.5292   $31.53   $31.55   $31.50  
  Purchase #7 $131.70   6.188%   $139.8496   $139.85   $139.85   $139.80  
  7 purchase totals = $863.84       $918.2426   $918.24   $918.20   $918.20